Workshop Compressed Air Distribution

[Andy Hall]

I use various types of compressed air tools in my workshop on a regular basis - nailers, sprayers, wrenches etc.

Long trailing hoses across the floor are a pain and a trip hazard so I want to put in permanent pipework around the walls and across the ceiling with outlets at strategic points.

So the question arises as to what to use. There appear to be three choices:

- Black steel tube (BS1387). This appears to be the common choice and pretty cheap, but probably the most difficult to work with, needing the pipe ends threaded etc.

- Copper tube. This would be convenient and easy to work. I did some Googling and found several references to doing this in the U.S., although one article mentioned that their type M tube (0.81mm wall thickness in 3/4") was not thick enough and that type K or L should be used - 1.65mm and 1.1mm in 3/4"

Translating this, table X tube in 22mm has a thickness of 0.9mm and table Y has 1.2mm..... so the table Y would appear to be thick enough but the commonly available table X is apparently not.

One article also suggested that brazing rather than soft soldering was needed.

Can anyone shed any light on this or suggest a source of table Y tube?

- Plastic pipe. John Guest make a blue coloured nylon pipe and fittings claimed to be for compressed air, and Durapipe make something similar in a special form of ABS, although I can't find a supplier at this point. Again referring to U.S. articles, plastics seem to be deprecated by the safety organisation, OSHA. The concern appears to be not so much whether it can stand the pressure, but more about what would happen on failure (e.g. from mechanical damage) - thought to be shards of plastic exploding everywhere. Since that could spoil one's weekend I feel rather dubious, easy to fit though this is.

Has anyone implemented a compressed air distribution system or know about any of these techniques?

The compressed air will be via a regulator and in the normal 6-8 bar range.

TIA for any useful data

.andy

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[Andy Hall]

That was also my concern. It would seem that major surgery would be needed if an extra outlet were required and not easy to do with the pipe in situ without taking lots of it down.

OK - seems to make sense, Richard. Which brands do you use and who supplies you?

Yes it does, thanks very much

.andy

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[Grunff]

I'm sure there's something wrong with the following idea, but since I can't think what, I'll tell you anyway.

I've used 25mm MDPE with nitrogen at 10 bar with no problems. Since MDPE is soft, it won't shatter. I used standard underground grab ring fittings (the single O ring type), with no leaks at the stated pressure.

[Andy Wade]

According to an IMI Yorkshire Copper Tube Ltd. brochure in my files, the max. working pressure for ordinary 22 mm 'Table X' tube is 51 bar. This is "in conjunction with Yorkshire fittings" (so soft soldered, presumably).

CDA publication 88 (on their Web site) gives a formula for working pressure (up to 65 deg. C): P = 20 * F * t / (D - t), where

P is max. wkg. pressure /bar F is design stress /MPa t is min. wall thickness /mm D is max. o/d /mm

From this you can deduce that with 22 x 0.9 mm tube at 7 bar air-line pressure the material is only being stressed to 8.2 MPa. The quoted tensile strength is 250 MPa, so the factor of safety would appear to be enormous (>30).

There was a longish thread here about this -- particularly w.r.t. the suitability of copper -- three or four years ago, maybe more. I can't remember what conclusion (if any) was drawn, but it's probably worth Googling for. Also this is the sort of thing the HSE are likely to have guidance notes about -- have you looked there?

[Andy Hall]

It's certainly substantial stuff and quite cheap. Presumably it would need supporting with clips quite regularly and then converting via fittings to provide outlets.

.andy

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[Andy Hall]

Do you mean the rubber type hose, Geoff? How do you do tees to do drops to the outlets or do you run a hose all the way to the compressor for each outlet and then use some form of manifold?

Thanks for the visit offer - might take you up on that?

.andy

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[Grunff]

It does need clipping every 50cm or so. As far as converting, I took the MDPE down to 22mm copper, and used compression fittings from there on.

[John Jardine]

The Durapipe 'Airline' system is installed in numerous installations worldwide, As the company is part of a large group, I assume the safety angle has been rigorously researched. It uses solvent jointing which is a *lot* easier than brazing or metal screwing. regards john

[Andy Hall]

Would you happen to know of a supplier, John?

I've Googled but nothing obvious comes up.

Otherwise I'll call them tomorrow....

.andy

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[geoff]

Steel "T"'s with adaptors. I'll try and take some photos tomorrow and email them to you

There is also a place jus behind us that specialise in compressors and fittings. You could pop over, and if you sounded enthusiastic, could probably pick their brains

[Mindwipe]

black steel tube..hassle to fit but will last forever once done right........don't forget the water drains though

[Andy Hall]

#

Thanks for that.

I'm also in the market for a new compressor. The small portable one that I have is OK for nailers but tends to run out of steam (air) for spraying and other higher volume applications. Do these guys have a web site or other details?

thanks Geoff

.andy

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[Andy Hall]

Thanks John

Am I right in my assumption that the regulator should go after the receiver and before the pipework, or is it normal practice to pipe directly from the receiver and install regulators at each outlet position? I notice that most belt driven compressors deliver at about 10 bar.

Also, do you happen to know what the typical method is to pipe from the receiver to the distribution system? Is this normally done with a hose because of the compressor vibration, or is there another way?

.andy

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[Andy Hall]

Point noted. If the main pipework is run near the ceiling with drops for outlets, is it reasonable to simply provide a downward pointing drain valve at each position?

.andy

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[Andy Hall]

I didn't realise that Costco did that type of stuff - never been to one. I'll check. I can fairly easily provide the necessary for their trade membership category. The individual one is rather curious in terms of who can join and who can't - I wonder who decided that?

.andy

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[geoff]

I can always buy it for you

[John]

In our case the compressor was a 600CFM Atlas Copco which charged the receiver directly to the compressors unloading pressure of 10 bar. The receiver had a Spirax-Sarco automatic float drain at the bottom but a parallel manual drain valve which the duty fitter had to operate every day to ensure the receiver was "dry" i.e. the auto drain was functioning. The receiver offtake was regulated down to 6 bar and piped around the factory via a ring main with all the offtakes "upwards" from the ring to avoid water carryover and auto drains at all low points and at the bottom of vertical risers. Again all auto drains were fitted with parallel test valves. Any "appliances" which needed less than 6 bar were individually regulated but in the main we used the air via solenoids to operate ram cylinders which were pretty non critical of pressure as long as there was sufficient to open or close the slide valves they operated. More exacting duty such as pneumatic positioners and the like did have their own regulators and lubricator/dryers

The receiver had a safety valve set to 12 bar IIRC and the lower pressure pipework had another one set to 7 bar. Both were capable of taking the whole output of the compressor.

We had a steel braided rubber flexible "bellows" between the compressor outlet and the start of the steel pipe section connecting to the receiver. This section of pipewrork could get pretty damn warm at times. The plastic distribution main came after the receiver

>

[Andy Hall]

I spotted the swan neck arrangements and assumed that this was to reduce water carry-over.

I spoke to Durapipe today (in fact it's part of Glynwed) and they are sending me a load of info and pricing as well as a complete design guide. There are quite a number of distributors including BSS, Pipeline Centre etc.

They did make the point that it's best to run the first metre or so in metal or other non-plastic hose for heat reasons. The other issue was to make sure that a compatible compressor oil is used. They list about 50.

.andy

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[geoff]

In message , Andy Hall writes

I bought some oil from ACL last week. I quoted the specified oil, and they said I could have that if I really wanted, but everyone always uses "this" oil (Silkolene SAE 50 IIRC) and it's cheaper.

BTW, no, they don't seem to have a website

I've taken some photos, and I'll send them tomorrow - too busy fitting a new cistern tonight to have time enough to do it

[Andy Hall]

OK, Geoff, thanks

.andy

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